Republican presidential candidate Herman Cain said on Friday that poor Americans will not have to pay the 9 percent flat income tax under his now-famous “9-9-9” tax reform plan.

During a speech in front of a vacant train depot in Detroit, the former Godfather’s Pizza CEO staunchly defended his signature tax proposal from critics who say it will raise taxes for lower-income Americans.

Cain’s plan would throw out the current tax system in favor of a 9 percent corporate tax, a 9 percent income tax and a new 9 percent national sales tax.

He said Friday that poor people under his plan would be exempt from paying the income tax.

The former pizza executive also unveiled his proposal on Friday for “opportunity zones” to help “renew distressed inner cities.” His proposal includes offering tax exemptions to businesses that invest in these zones.